Transglutaminase-like superfamily. This family includes animal transglutaminases and other bacterial proteins of unknown function. Sequence conservation in this superfamily primarily involves three motifs that centre around conserved cysteine, histidine, and aspartate residues that form the catalytic triad in the structurally characterized transglutaminase, the human blood clotting factor XIIIa'. On the basis of the experimentally demonstrated activity of the Methanobacterium phage pseudomurein endoisopeptidase, it is proposed that many, if not all, microbial homologues of the transglutaminases are proteases and that the eukaryotic transglutaminases have evolved from an ancestral protease.